Plasma glycerol: potential evidence of cold adaptation in green sea turtles (Chelonia mydas)

Supposed torpid or overwintering green sea turtles (Chelonia mydas) have been reported several times in the past 60 years in the Gulfs of California and Mexico. Each winter along the Atlantic coast of the United States,... [ view full abstract ]

Supposed torpid or overwintering green sea turtles (Chelonia mydas) have been reported several times in the past 60 years in the Gulfs of California and Mexico. Each winter along the Atlantic coast of the United States, hundreds to thousands of sea turtles strand due to cold stun syndrome. However, there has been little scientific research into the potential cold adaptations of sea turtles. Glycerol has been identified as a cryoprotectant and important metabolite in studies of both invertebrates and vertebrates; the objective of this study was to determine the presence of glycerol and differences in concentration between normal and cold stun affected green sea turtles. Heparinized plasma samples from cold stun affected (n = 11) and normal (n = 10) green sea turtles were analyzed via proton nuclear magnetic resonance spectroscopy. Relative glycerol concentrations were significantly greater in the cold stun affected group (p = 0.01; one-sided paired comparison random permutation test, R=1000). In insects, glycerol is produced from glucose in fat body tissue and its accumulation appears to be anticipatory of colder temperatures. In vertebrates such as black bears (Ursus americanus), glycerol (also derived from fat) is used for amino acid and protein production, gluconeogenesis, and lipogenesis. Utilization of glycerol during hibernation has also been shown to prevent uremia. Further research is necessary to identify additional biomarkers and pathways related to cold adaptation, potentially including radio-labeled glycerol, and to determine the fate of glycerol in cold stun affected green sea turtles. The accumulation of glycerol in the plasma of cold stun affected green sea turtles suggests its use as a cryoprotectant and/or active metabolic adaptation to cold temperatures.